Xml – xsd:boolean element type accept “true” but not “True”. How to make it accept it

You need to change your XML instance. Your current one says that there is a type called description in the namespace http://www.namespace.org/recipe. However, in your XSD definition, the only types exposed in that namespace are called recipe and descriptionType.

So either define a type called description in the XSD schema, or change your instance so you are referencing the recipe type correctly:

<?xml version="1.0" encoding="utf-8"?>
<r:recipe
  xmlns:r="http://www.namespace.org/recipe">
  <description>
    <title>sugar cookies</title>
  </description>
</r:recipe>

UPDATE This is only half the solution - the other half is in @Aravind's answer here: https://stackoverflow.com/a/8426185/569662

You can create a wrapper schema and import both namespaces. AB.xsd:

<?xml version="1.0" encoding="UTF-8"?>
<schema elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema">
    <import namespace="http://www.example.org/A" schemaLocation="A.xsd"/>
    <import namespace="http://www.example.org/B" schemaLocation="B.xsd"/>
</schema>

Then:

xmllint --schema AB.xsd ab.xml
<?xml version="1.0" encoding="UTF-8"?>
<a:someType xmlns:a="http://www.example.org/A" xmlns:b="http://www.example.org/B" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.example.org/A A.xsd                             http://www.example.org/B B.xsd">

            <b:person>
                <b:firstName>Mary</b:firstName>
                <b:lastName>Bones</b:lastName>
            </b:person>

</a:someType>
ab.xml validates